In high speed automation, vacuum valves are capable of building a vacuum and shutting off a vacuum quickly. Many processes are gated by the speed at which this can occur. One example of such an application is vacuum gripper devices used to pick up and move mail, envelopes, and/or paper. Conventional vacuum valves must be replaced frequently due to short life spans.
One type of conventional vacuum valve is a packed spool valve. The spool is generally a cylindrical piece located in the center of the valve that is actuated back and forth by compressed air. Sealing surfaces on the spool, e.g., vulcanized rubber, slide back and forth across a highly polished sleeve, changing the connection paths from input to output as the spool moves.
A conventional packed spool valve is typically designed for air filtered to 40 microns. However, 5 micron filtration is desirable for demanding applications and long valve life. Due to the nature of the application and the very high speed switching of vacuum to vent and corresponding vacuum decay times needed, the incorporation of a filter in order to achieve this level of filtration is neither possible nor practical. Also, the incorporation of a filter to protect the inner workings of the packed spool valve would necessitate a large preventative maintenance operation to change up to 10 separate filters on each machine in a very short replacement cycle. As a result, the internal working components of the packed spool valve are subject to a high degree of particulates of varying size and type, the majority being paper dust, which is very abrasive and also which builds-up inside the valve causing it to leak or otherwise fail due to contamination. The sealing of the packed spool valve is dependent upon the close mating of the vulcanized spool with the inner surface of the sleeve. Conventional packed spool valves last about three to four months in operation before the level of contamination causes them to fail.